Noise dosimeter

ABSTRACT

A noise dosimeter having noise pick-up means for generating an analog signal in correspondence to picked-up noise, signal processing means for generating pulses in correspondence to the analog signal, and means for adding and storing the pulses.

United States Patent 91 Widegren et al.

[ 51 Feb. 5, 1974 NOISE DOSIMETER [76] Inventors: Lars H. Widegren, Larargatan 14,

981 ()0; Tage O. Keskitalo, Knavagen 9, 981 00, both of Kiruna, Sweden [22] Filed: May 15, 1972 [21] Appl. No.1 253,038

[52] US. Cl. 181/.5 AP [51] Int. Cl. G01h 3/12, GOlh H08 [58] Field of Search 181/.5 AP, .5 R, .5 D;

[56] References Cited UNITED STATES PATENTS 3,696,206 10/1972 lda 181/.5 AP

2/1966 Church 181/.5 AP 5/1961 Stewart 181/.5 AP

Primary Examiner--Benjamin A. Borchelt Assistant Examiner-J. V. Doramus Attorney, Agent, or Firm--Elliott l. Pollock et a1.

[57] ABSTRACT A noise dosimeter having noise pick-up means for generating an analog signal in correspondence to picked-up noise, signal processing means for generating pulses in correspondence to the analog signal, and means for adding and storing the pulses.

1 Claim, 9 Drawing Figures NOISE DOSIMETER dosimeter.

The effects of noise are in many respects unknown. However, it has been proved that a strong noise gives rise to psychological as well as physiological effects on human beings for example effects on the blood circulation and stomach and intestine activities. The type and strength of the individual reactions do, however, vary considerably. Some persons who during a long time are subjected to strong noise can become aggressive, while some very easily become resigned. Most known of the effects of noise and perhaps the most serious is noise deafness. This is caused by mechanical damage to the auditory organ, which damage usually appears after a long stay in a strongly noisy surrounding.

Unfortunately the ear does not warn a person subjected to noise by pain perceptions until the limit for auditory damages is more than exceeded. Two thirds of the industry workers are estimated by medical experts to have more or less impaired hearing-powers due to noise. The length of the time during which a human being is subjected to noise is a very important factor when judging the risk for hearing damages and the extent of the damages, if any.

The most usual method today when surveying the noise level on our places of work is measurements of sample test type. However, the noise level can vary very strongly during a shift, and sample test measurements, thus, can be afflicted with quite serious faults among other things due to the fact that it is not possible at these measurements to consider the time of exposure which is a very important factor. Since the questions of noise has started to more and more come to the front among todays environmental questions, a need has arisen for a device which can give an indication of the amount of noise which an individual is subjected to during a definite period of time.

Thus, the purpose of the present invention is to provide a device by means of which such storing can be carried out for noise signals. By means of the device defined according to the invention, noise measurements can be carried out and integrated over a certain period of time, whereby an indication is obtained of the total amount of noise during the period of time in question. The means by which the defined end is attained are defined in the attached claims.

According to the inventive idea on which the present invention is based, it is possible to store energy supplied in the form of signals preprocessed to unitary information pulses, the contents of said signals bein arbitrary. According to the invention, the signals can be pickedup in due order by a pick-up device during a time interval selected suitable for the current measurement requirements, whereupon the signal processed in a suitable manner successively charges or discharges an energy accumulating means, the energy contents of which is measured at suitable times by means of an instrument known per se. As an example, this can be illustrated by storing noise appearing during a certain time interval which noise is measured in such a manner that noise impulse signals proportional to the effective value of the appearing noise are supplied successively to an accumulating device, for example, a capacitor which thereby is charged successively in such a manner that the capacitor voltage is a measure of the noise dose. The capacitor voltage is read for example either on a pointer instrument or a digital instrument or registered by a writer or something similar after a suitable period of time. The capacitor is then discharged whereupon a new period of measurement can immediately be commenced. It is also possible to let a capacitor be charged from the beginning and then let it be discharged in correspondence to noise impulses supplied.

The high noise levels for example within industry and transportation have led to an increased number of noise damages. Attention has lately been more and more paid to this state of things and it has been found that it is necessary that the noise and, more exactly the energy of the noise (i.e. the integrated effect) is kept under a certain level in order not to harm people subjected to the noise. According to the present invention, a direct reading instrument is defined, which instrment can be used in this connection.

Among the difficulties encountered when it comes to designing an instrument of the type in question can be mentioned the problem that the instrument must have a large dynamic range, according to the present standards between dB and dB. Moreover its size has to be small and still the instrument has to be robust and durable. The microphone used to pick-up the noise has to be stable.

The invention will be described more in detail below with reference to the attached drawings on which FIG. 1 is a block diagram showing the general principles of the inventive idea, FIG. 2 is a circuit diagram showing one of several obvious alternative possibilities to realize a storing unit which can used in the invention, FIG. 3 is a block diagram showing a device designed according to the principals of the invention which device herein after will be called a noise dose meter since it indicates the noise dose i.e. the noise level multiplied by the time of exposure, FIGS. 4, 5 and 6 show examples of some of the circuits in said noise dosimeter, FIG. 7 is a combination of the circuits of FIGS. 2 and 4-6, FIG. 8 shows a circuit that warns when the allowed noise dose has been attained, and FIG. 9 shows a circuit that warns against dangerous noise level.

The block diagram shown in FIG. 1 comprises, from the left, a signal converter 1 which is intended to convert an arbitrary magnitude to an equivalent electric signal, a device 2 for signal processing, which device in the simplest case comprises a voltage-to-frequency converter, a storage device 3 which translates incoming information pulses to amounts of charge corresponding to the individual pulses, the amounts of charge being added and stored in a memory device, and a read-out device 4 comprising for example a pointer instrument, a digital instrument, a writing device or the like.

The circuit shown in FIG. 2 comprising a storage unit according to the invention includes in the shown embodiment three resistors 5, 6 and 7 which can be selected arbitrarily in a manner suitable for the current application, a transistor 8, two diodes 10 and 11, two capacitors 9 and 12, the capacitor 9 determining the amount of charge which for each pulse is stored into the storage capacitor 12, and a zener-diode 44. The function of the device according to FIG. 2 is as follows.

Assume that the storage capacitor 12 is empty from the beginning and that a feed voltage is connected between the conductor marked and ground which is also the negative pole. The transistor 8 works as a switch and is at this moment in its non-conducting state. The capacitor 9 will be supplied with a charge corresponding to the current measurement application via the resistor 7. When an input signal in the form of a pulse is supplied via the conductor A, the transistor 8 will conduct and the capacitor 9 is short-circuited via the diode 11 which is to provide a closed circuit when the capacitor 9 is discharged. When the pulse ceases, the transistor 8 is immediately returned to its nonconducting state and the voltage across the capacitor 9 increases with a jump to the value of the battery voltage and a definite amount of charge is fed via the diode into the storage capacitor 12. Each time this is repeated, a certain amount of charge is transferred to the capacitor 12. The amount of charge is determined by the capacitance of capacitor 9 and the voltage across the same, the voltage being made up of the battery voltage minus the voltage already stored in the capacitor 12, whereby a logarithmic charging process is obtained in capacitor 12 in this connection. The purpose of the zener-diode 44 is to keep the voltage constant despite changes in the battery voltage. It is of course also possible to have an arrangement which during the whole charging process gives a constant amount of charge which is stored for each pulse. In this manner a linear charging process is obtained.

The block diagram of FIG. 3 shows a practical application of the block diagram according to FIG. 1 in the form of a noise dosimeter Le. a device for measuring a noise dose in which the storage process described above is utilized. From the left, the blocks in FIG. 3 represent a microphone 13, an amplifier 14 with a circuit 48 warning at a dangerous noise level, a weighing filter l5with a connectable filter 45 simulating an auditory protection, a logarithmic/doubling circuit 16, an inverting amplifier 17, an antilogarithmic circuit 18, an integrator 19, a voltage-to-frequency converter and a storing unit 21 with a circuit 47 that warns when a loud noise dose is attached. Moreover there is a block 22 corresponding to a read-out device which can be built in or separate.

For a more detailed description of the separate parts of the noise dosimeter and the function of the noise dosimeter reference is made to FIGS. 4-6. The blocks 13 and 14 included in the block diagram according to FIG. 3 representing a microphone and an amplifier, respectively, are quite conventional and will not be described more in detail, while the block 48 will be described in connection to FIG. 9. As to the block 15 representing a weighing filter, it should only be mentioned that, according to present standards of measurement, it should be a so-called dB(A) filter. The filter can of course be exchanged if the standards should be ammended and, moreover, several filters can eventually be inserted in parallel for alternative possibilities of measurement as for example the filter 45 corresponding to an applied auditory protection which filter is connected by means of a switch 46. The block 16 representing a logarithmic/doubling circuit is shown more in detail in FIG. 4 and comprises a balanced and compensated opera tional amplifier 23, an input resistor 24 and two series connected diodes 25, 26 and 27, 28, respectively, in the feed back path for each current direction.

By this connection, the amplification of the operational amplifier will equal twice the logarithm of the input signal and, due to the manner in which the diodes of the feed back path are connected, both positive and negative input signals will be processed in the same manner so that the full information contents will be obtained 0n the output. The output of the circuit according to FIG. 4 is connected to the input of the circuit according to FIG. 5 corresponding to the blocks 17 (inverting amplifier) and 18 (antilogarithmic circuit).

The circuit according to FIG. 5 comprises a balanced and compensated operational amplifier 29, an input resistor 30, a feed back resistor 31, a balancing potentiometer 32 and antilogarithmic diodes 33 and 34. This circuit functions in such a manner that negative output signals from the operational amplifier 23 are supplied directly to the antilogarithmic diode 33, while positive signals are inverted in the operational amplifier 29 before they are supplied to the antilogarithmic diode 34. By means of the input resistor 30, the feed back resistor 31 and the balancing potentiometer 32, the operational amplifier 29 can be adjusted to the amplification value 1 with great accuracy.

The circuit according to FIG. 6 corresponds to the blocks 19 (integrator) and 20 (voltage to frequency converter) shown in FIG. 3 and comprises a balanced and compensated operational amplifier 35, an integrating capacitor 36, a thyristor 37, a unijunction diode 38, resistors 39, 40 and 42, a potentiometer 41 and a diode 43. The function is such that the output signal from the antilogarithmic circuit which signal is the input signal in the circuit according to FIG. 6 is integrated in the capacitor 36 to a voltage determined by the unijunction diode 38, whereupon a pulse which appears across the resistor 39 when the unijunction diode 38 has reached its breakdown voltage reaches the thyristor 37 which fires and short-circuits the capacitor 36 whereupon the process is repeated. The potentiometer 41 and the resistor 42 voltage feed the diode 43 which is connected in such a manner that the temperature dependence of the logarithmic and antilogarithmic diodes is compensated. It should be pointed out that the circuits according to FIGS. 4-6 merely show examples of how the described functions can be realized, and corresponding circuits can, of course, function as well with other connections suitable for the purpose.

FIG. 6 shows a combination of the circuits according to FIGS. 2, 4, 5 and 6 described above. Also in this combination components, the purpose of which are to provide the circuits with suitable voltages, provide phase compensation and zero balancing etc. have been left out, since the purpose has mainly been to illustrate the signal processing.

The voltage across the capacitor 12 is a measurement of the noise dose that the person carrying the noise dosimeter has been subjected to. To warn the carrier when the allowed noise dose has been attained, the circuit shown in FIG. 8 is connected across the capacitor 12. This circuit comprises a field effect transfer 49, three transistors 50, 51 and 52, a warning lamp 53 and eight resistors 54-61. The field effect transistor 49 and the resistor 54 form a voltage divider that at the voltage corresponding to the allowed maximum noise dose across the capacitor 12 supplies the transistor 50 with the base current necessary to make this transistor conducting. The transistor 51 that normally is conducting, is thereby blocked, whereupon the transistor 52 will conduct and the lamp 53 will be fired as an indication of that the allowed maximum noise dose has been attained. The lamp 53 can of course be exchanged for an acoustical or other signalling device.

It is also important that he who stays in too high a noise level is informed about this. To provide this, a circuit similar to the circuit shown in FIG. 8 is connected via the circuit shown in FIG. 9, to, for example, the output of the amplifier 14. The connecting circuit according to FIG. 9 comprises a diode 62, a resistor 63 and a capacitor 64. When the current from the amplifier 14 through the diode 62 is so large that the voltage across the capacitor 64, despite a controlled leakage through the resistor 63, amounts to the value where the field effect transistor 49' drives the transistor 51' to conduction, the lamp 53 corresponding to the lamp 53 will be fired as an indication that the present noise level is too high. It should be pointed out that it is also possible to connect the circuit shown in FIG. 9 to the input of the storage unit 21.

For the case in which it is desired to, at the same time, measure noise doses within different frequency ranges such as infra sound and ultra sound, the noise dosimeter shown in FIG. 3 should be completed with identical dosimeter connections tuned to the respective frequency range.

The noise dosimeter described above, which dosimeter merely is an example of the application of the invention, is intended to be an instrument by means of which it is possible to register the amount of noise that an individual is subjected to for example during a work shift, and it is so defined that a stored value is directly relative to present standards of damage. The meter can of course be adapted to any amended standards or to other measuring ranges such as disturbing noise where the standards are based on other sound level ranges. By storing the result of the measurement according to the invention the measurement can be carried out over a very long period of time at the same time as the result is available for reading at arbitrary times. Moreover, the storing can be continued during read-out and after the read-out but can also be stopped so that a new period of measurement can be commenced.

The inventive idea has arisen from the need of a storing process for, among other things, a noise dosimeter which gives greater accuracy and a simplified use than for example current electro-chemical indicators but still makes a small and light instrument possible which can be carried individualy, for example as a unit built into a protective helmet, without constituting an obstacle during work.

We claim:

1. A noise dosimeter comprising in combination,

a microphone responsive to noise for generating a corresponding electrical noise signal,

filter circuit means receiving said electrical noise signal,

squaring circuit means including in series a logarithmic-doubler circuit means followed by an antilogarithmic circuit means,

said squaring circuit means connected to receive the output of said filter circuit means,

polarity inverting circuit means operatively associated with said squaring circuit means and responsive to signals of one polarity to provide output signals of the opposite polarity to ensure thereby that the output of said squaring circuit means is of the same predetermined polarity irrespective of the polarity of the input signals applied thereto,

an integrator for integrating the output of said squaring circuit,

a voltage-frequency convertor responsive to the output of said integrator,

and a pulse summing circuit for summing the output of said converter.

izgyggfio UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,789, 952 Dated February 5, 1974 Inventor(s) LARS H. WIDEGREN and TAGE O. KESKITALO It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Foreign Application Priority Data a o o o o I I Signed' and sealed this 9th day of July 197A.

(SEAL) Attest:

McCOY M. GIBSON, JR. Attesting Officer 0 MARSHALL DANN Commissioner of Patents 

1. A noise dosimeter comprising in combination, a microphone responsive to noise for generating a corresponding electrical noise signal, filter circuit means receiving said electrical noise signal, squaring circuit means including in series a logarithmic-doubler circuit means followed by an anti-logarithmic circuit means, said squaring circuit means connected to receive the output of said filter circuit means, polarity inverting circuit means operatively associated with said squaring circuit means and responsive to signals of one polarity to provide output signals of the opposite polarity to ensure thereby that the output of said squaring circuit means is of the same predetermined polarity irrespective of the polarity of the input signals applied thereto, an integrator for integrating the output of said squaring circuit, a voltage-frequency convertor responsive to the output of said integrator, and a pulse summing circuit for summing the output of said converter. 